Surface metal-ion-functionalized carbon dots and their application in pH sensing

Abstract

In recent years, it has witnessed a rapid development of the fluorescent carbon dots (CDs) due to their unique optical properties and wide range of applications. However, difficulties in synthesizing long wavelength-emitting CDs have been the major drawback of CDs, which limited their applications in fields such as bioimaging and carbon-based white light-emitting diodes. Herein, on the basis of surface electron state engineering, we prepared surface metal-ion-functionalized CDs by treating solvothermally synthesized CDs with alkali metal aqueous solutions (LiOH, NaOH or KOH). Especially, we focused the CDs treated with LiOH solution (Li-CDs) because these CDs’ absolute photoluminescence quantum yield is as high as 34% in dilute ethanol solution under 550 nm excitation compared with those treated with NaOH or KOH solutions. The electron transport effect of alkali metal ions was confirmed. Moreover, the obtained Li-CDs show high optical pH sensitivity within pH values 1–4.5 and were applied to pH sensing. This work not only proposes a feasible and controllable method to construct long wavelength-emitting CDs, but also shows the application potentiality such as pH sensing devices.